1. Field of the Invention
This invention relates to systems and methods for introducing cable and items connected thereto into a wellbore and, in certain particular aspects to a system with a capstan drive apparatus for facilitating the introduction of cable into a wellbore reducing or eliminating the need for added weight, e.g. sinker bars.
2. Description of Related Art
Various operations in a wellbore require the raising and lowering of various tools and equipment on a cable within the wellbore. For example, in wellbore logging operations a logging system is hung from a cable and moved into and out of the wellbore by raising and lowering the cable. In various prior art wellbore cable systems, the tools or equipment for introduction into and movement within a wellbore are connected to one end of the cable and the other end is connected to some type of winch or other raising/lowering system. In many systems, the cable is passed over one or more sheave wheels positioned between the winch and the wellbore. It is common for one such sheave wheel to be secured to a derrick or rig above the wellbore as well as one such sheave wheel mounted below on the ground or on a rig platform. Such systems typically employ a fluid pressure control system to counterbalance the pressure of fluid in the well which can oppose the introduction into the wellbore of the cable and items connected thereto. Often weight (e.g. sinker bars) is added to the items hung from the cable to counter upward fluid pressure in the wellbore and to pull the cable through the fluid pressure control system. This added weight requires a corresponding increase in height of a lubricator used above the wellhead between it and the sheave wheel(s). The lubricator is long enough to hold all of the tools going downhole, including the sinker bars.
In the prior art systems described above the height of an entire system above the rig platform can be substantial, e.g. forty-five or more feet. The problems associated with such high systems were addressed in U.S. Pat. No. 5,188,173 which discloses a cable system for use in well cable operations in association with a rig at the surface, the system having a pressure control device for counterbalancing the fluid pressure from the well; a high pressure chamber through which the cable passes; and a cable sheave wheel incorporating the chamber. By using the cable sheave wheel in its own pressurized chamber and pointing the chamber downward, an effort is made to reduce overall system height. The sheave wheel of the systems of U.S. Pat. No. 5,188,173 has a groove for receiving and holding the cable.
There has long been a need for an effective and efficient system for introducing cable into a wellbore whose overall height is reduced as compared to the height of prior art systems and which adequately moves the cable into the wellbore. There has long been a need for a system which pulls the cable through a pressure control device in high pressure wells and thus reduces or eliminates the need for sinker bars thereby reducing rig up height.